Roller cone bit used in the oil and gas drilling industry typically have sealed ball bearings that are lubricated from a lubricating system. Grease is often used as the lubricant. Of the bearing components, the bearing seal typically has the lowest mean time between failure, so that the bearing seal effectiveness typically determines the life of the bearing system. As the seal wears, the grease may become contaminated with drilling mud and water, which are gradually introduced into the lubrication system. Accordingly, the amount of contaminant fluid within the lubricant indicates the effectiveness of the seal, and when the contaminant reaches a predetermined limit, continued drilling must cease, lest a bearing failure occur that can leave one or more roller cones at the bottom of the borehole and require a costly fishing operating to retrieve them.
Prior art techniques are known for sensing an impending bearing failure due to a bearing seal failure. In some cases, bearing seal failure is gradual, but in other cases, bearing failure may occur catastrophically with little to no warning. Prior art methods of detecting seal failure may not be sensitive enough predict an imminent seal failure or responsive enough detect a seal failure and rapidly communicate such condition before significant bearing damage occurs. Accordingly, it is desirable to detect seal failure of a roller cone bit in real time.